This invention relates to recording heads in magnetographic printing and more specifically to recording head arrangements and fabrications enabling the use of substantially lower write currents and flat construction, which improve reliability, speed of recording and cost effectiveness, as well as lend themselves to mass-producibility. This invention in particular relates to improvements in the recording head design described in U.S. Pat. No. 4,025,927 to A. Nelson, the subject matter of which, in so far as it is pertinent to this invention, is incorporated by reference herein.
Although the recording scheme of the above-mentioned patent lends itself to the design and fabrication of recording heads having a multiplicity of recording elements of very fine structure capable of highly articulate recording, wherein such fabrication could utilize the so-called "etch foil" technology as described in said patent, such a recording head normally requires relatively high recording current to effect satisfactory magnetic recordings. The requirement of relatively high recording current leads to several engineering design concerns.
The first deals with the generation of possibly destructive heat at and near the recording zone when recording at high speeds. As such, a reduction in the electrical resistance of the individual recording elements would be appropriate.
The reduction of the electrical resistance of the recording elements leads to a second concern, namely an increase in the circuit time constant, L/R, which in turn reduces the recording speed. To overcome this, one is led to utilize sophisticated and/or inefficient driving schemes.
A third concern involves the need for large and relatively expensive driving components providing the high recording current. In addition to increased expense, the large driving components create packaging and other problems, especially for wider recording head designs.
Furthermore, to define the recording zone Nelson requires the creation of a physical virtually square notch in each of the recording elements. To achieve a well defined recording zone, the height of this notch must be relatively large as compared with the width of the recording elements, in the vicinity of the recording zone (e.g. in a recording head with 250 recording elements per inch, the height of the notch typically would be approximately 1.5.times.10.sup.-3 in. and the width of recording element is 2.times.10.sup.-3 in., with a typical recording zone length being on the order of 3.5.times.10.sup.-3 in.). In high resolution recording heads, creation of this notch, within such specifications, can become quite difficult in terms of mass production and, therefore, is of concern.
What is desired is an improved recording head arrangement capable of highly articulate recording with substantially smaller recording currents, and such is a principal objective of this invention.
What is also desired is an improved recording head arrangement having virtually flat construction and high recording zone definition and yet readily lends itself to mass producibility, and such is another principal objective of this invention.
The above-mentioned concerns and are solved in accordance with the improved method and apparatus of this invention for magnetic recording on a magnetizable medium wherein there is provided adjacent to at least one major surface of each current-carrying conductor constituting a write element of a recording head, at the recording zone of said element, a material which effects a substantial reduction in the reluctance of the magnetic circuit associated to the recording zone of said conductor.
Thus there is provided by the present invention a multi-channel magnetic recording head in which each channel includes a conductive writing element having a recording zone, wherein the writing elements consitute a plurality of elongated conductor strips each substantially parallel to one another and having predetermined width and thickness at least in the recording zone associated thereto, with each said conductor strip having a first surface arranged for facing a magnetizable recording medium and also a second surface, wherein a relatively high permeability, high magnetically saturable material (i.e. a material having a high magnetic saturation level or density) is contiguous to the second surface of each conductor strip at the recording zone.
In accordance with the invention it is particularly advantageous to further define the recording zone associated to each of the recording elements of the recording head. In connection therewith the invention provides an improved method of recording on a magnetizable medium via at least one current-carrying conductive element having a recording zone associated thereto, wherein the improvement comprises reducing the magnetic circuit reluctance outside the recording medium around said conductor at least at the recording zone wherein the reluctance is reduced by placing a relatively high permeability, high magnetically saturable material adjacent to at least the surface of the conductive element which faces the recording medium and other than at the recording zone.
An example of high permeability, high magnetic saturation material suitable for use in accordance with the present invention is an epoxy carrier with a pigment of of carbonyl iron (e.g. GAF product SF8). An alternative suitable material would be the Emerson & Cuming product CR124.
Further in accordance with the invention there is provided a flat, planar type articulate structure which can be constructed for example by metalization techniques utilized in fabricating large current integrated circuits, and thus is mass-producible with high reliability. In addition, the recording head area encompassing the recording zones of each of the recording elements can be as thin as a few microns and thus could be as much as fifty times as wide (or long) as it is high (or thick). This is in contrast, for example, to the recording head of the aforementioned Nelson patent, in which a notch is required which is roughly half the width or length, or even equal to the width or length, of a recorded pixel, i.e. a few mils wide.
In addition to the present invention effecting a substantial reduction in the recording current utilized in the conductive recording elements, the need is obviated for a geometric shift of the current flow path at the record zone toward the recording medium to articulately define the recording zone of each recording element. The present invention achieves a highly articulate shift in the magnetic field around the current-carrying conductor constituting the recording element, in localizing the recording function thereof without for example the notch construction depicted in the aforementioned patent.
Moreover, in constructing planar recording elements in accordance with the present invention, smaller "writing gaps" or recording zones, i.e. the portion of the conductive recording elements generating sufficient magnetizing field to effect recording on a magnetizable medium, are readily realizable, providing substantially sharper magnetic field intensity transitions and leading to higher resolutions. An additional advantage of recording heads constructed in accordance with the present invention is that the recording medium may now be situated very close to the recording elements of the recording head.
A further advantage of the present invention is that with thin film metalization construction techniques, one can with great accuracy selectively place regions of magnetic thin film behind the conductors, i.e. the major surface of the current-carrying recording element facing away from the recording medium (which is the surface normally attached to or otherwise contiguous with a support material or substrate usually in the form of a mandrel).
An additional feature of this invention is the capability of the material placed at the recording zone to provide a pre-biasing magnetic effect. By this the recording function is augmented locally; as such, this leads to a reduction in the recording current needed. More particularly, the material behind the recording element at the recording zone may be a relatively hard magnetic material (i.e. having a relatively high magnetic remanence as well as relatively high magnetic saturability), such as iron oxide. To derive the pre-biasing effect, one need only apply an initial current in each conductive element of sufficient level and duration to effectively achieve a saturation of the magnetic material behind said conductors at the recording zone, whereby local magnetization of said material occurs. Thereafter, whenever the conductive element is energized, this local premagnetization will assist in the recording function, although by itself the pre-biasing magnetic field is insufficient to effect a recording on the magnetic medium. As a result, lower recording current may be employed in the recording elements to effect satisfactory recording on the recording medium.